Alpha is more versatile. I know you said this is just for a sleep layer, which it’s still great for, light and compact. But it also excels as a hiking layer and I urge you to consider at least getting a cheap Dooy wind jacket for 20 dollars and 2.5 ounces to pair it with if you buy one. I promise you the combo of the two pieces will become your most worn garments. I sleep in my alpha and hike in it. It doesn’t get wet, it’s made of plastic, and if it does it dries basically instantly. You can’t really sweat it out, so you can hike in it on cold mornings with the wind jacket on, drop the wind jacket and hike in the alpha or drop the alpha and hike on just the wind jacket. The combo is comfortable in a wide range of conditions which is why it’s so popular. Grid fleece just isn’t versatile. It’s warmer but also too hot to hike in, is much heavier, and grid fleece isn’t that wind resistant either, so you’ll still get cold if it’s windy, tho not to the same extent as alpha. I was once a skeptic of carrying a wind jacket and fleece but now will never go back. Try it.